Intergranular corrosion of Zn-free and Zn-microalloyed Al-xCu-yLi alloys

The influence of 0.42 and 0.72 wt.% Zn on the intergranular corrosion (IGC) of Al-3.7Cu-1.15Li-0.5Mg and Al-2.7Cu-1.7Li-0.3Mg alloys (representing different Cu/Li ratios) was investigated. IGC dependence on ageing time was studied and a primitive IGC diagram established. With ageing, the potential of the Al-xCu-yLi alloys lowered due to precipitation, accompanied by grain boundary precipitate coarsening. Concomitantly, corrosion mode evolved with ageing from pitting and local IGC (early ageing), general IGC (under-aged), local IGC (near peak-aged) and pitting (over-aged). Of key interest is that Zn additions remarkably decreased the IGC sensitivity of the Al-2.7Cu-1.7Li-0.3Mg.